1. Field of the Invention
The present invention relates to a tool holder clamp device for spindle of a machine tool, and particularly, to a tool holder clamp device for spindle of a screw-fastening type, as well as to a spindle apparatus including such a tool holder clamp device.
2. Description of Relevant Art
As a tool holder clamp device for a spindle for high-speed rotation, there has been proposed in Japanese Patent Application Laid-Open Publication No. 10-76413 (1998) a device in which unbalancing factors are eliminated to suppress increase of inertial force in rotation of a spindle.
This device is a screw-fastening type in which a spindle has a taper hole formed in a distal end part thereof and a tool holder has a shank portion adapted for insertion to and draw-out from the taper hole, and by which the shank portion is clamped in a screw fastening manner. The screw-fastening type tool holder clamp device comprises a clamp bolt member, which has a threaded part provided in a central through-hole or hollow of the spindle communicating with the taper hole and adapted to be screwed in a threaded hole axially formed in the shank portion of the tool holder and which fixes the tool holder by fastening the shank portion by means of the threaded part, and a drive shaft body (as a draw-bar member), which is provided in the central through-hole and axially movable to engage with the clamp bolt member for drive connection therewith to thereby drive the clamp bolt member into rotation. When the spindle rotates, the drive shaft member is separated from the clamp bolt member so that unbalancing factors of the spindle are eliminated, and the spindle has a reduced weight.
In such a screw-fastening type tool holder clamp device, as a clamp bolt member is incorporated to a spindle and not allowed to axially move, when the clamp bolt member is driven into rotation for attachment or detachment of a tool holder, it is necessary to change an axial relative position between a spindle apparatus and the tool holder in accordance with a screw lead.
Therefor, in use of an automatic tool exchange device to effect automatic exchange of tool, there is necessitated a synchronous control between the clamp bolt member to be rotated and the spindle apparatus to be axially moved in conjunction therewith.
However, the clamp bolt member to be separable from a drive shaft body, which serves as a body of rotary drive to rotate the clamp bolt member, is connected thereto by a mating between a polygonal column and a polygonal hole for example, and a quantity of rotation of the rotary drive body does not always coincide with that of the clamp bolt member, so that the rotation quantity of the rotary drive body cannot be based on for control of a rotation quantity of the clamp bolt member. It is thus difficult for a quantity of rotation of the clamp bolt member and a quantity of axial movement of the spindle apparatus to be associated with each other for synchronous control therebetween, with the result that such a conventional screw-fastening type tool holder clamp device is unable to cope with the use of an automatic tool exchange device.